Method of stabilizing an endoscopic assembly

ABSTRACT

Methods and apparatus for direct visual rhizotomy using an elongated tubular sheath. The sheath includes: a proximal end configured to removably receive a cannula; a distal end; a horizontal shaft having a longitudinal axis extending between the proximal end and the distal end; a first cut-away generally defining a first plane at the distal end, the first cut-away characterized by a first angle relative to a vertical plane; and a second cut-away generally defining a second plane at the distal end, the second cut-away characterized by a second angle relative to a horizontal plane. The sheath further includes an endoscope camera disposed at the distal end, the camera having a line of sight substantially orthogonal to the first plane.

RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 15/163,619, filedMay 24, 2016.

TECHNICAL FIELD

The present invention relates, generally, to methods and apparatus forfacilitating direct visualized rhizotomy (DVR) procedures and, moreparticularly, to a low profile DVR sheath configured for secureplacement on the transverse process.

BACKGROUND

Other than the common cold, back pain is the number one reason peoplevisit a doctor in the United States. There are three principle sourcesof back pain: i) joint pain (40%); ii) pain from a nerve root (40%); andiii) disc pain (20%). Mature and robust treatment regimens have beendeveloped for disc and root pain including surgical, non-surgical, andepidural modalities. Effective treatment for joint pain has only emergedwithin the last decade, and to the present day remains elusive with onlymoderate success.

Spinal joint pain occurs in the facet joint between adjacent vertebrae.The five facet joints on each side of the lumbar spine produce painsignals when they become arthritic or because of injury due to trauma,with 90% of cases occurring at the L4/L5 and L5/S1 junctions. The spinalnerve root, which runs through the spinal column, innervates thevertebrae with two small medial nerve braches, called twigs. Each twigextends across a transverse process associated with each vertebral body.Nerves can have three types of fibers: motor, sensory, and autonomic.The twigs at issue are only sensory; that is, their sole function is totransmit pain via pressure, chemical, and pure pain receptors.

Consequently, cutting a medial branch of the spinal nerve root (thetwig) permanently prevents it from transmitting pain signals from thejoint to the brain, without compromising any motor or autonomicfunctionality; that is, cutting the twig stops the pain with nocorresponding degradation in nerve function. Pain doctors in the medicalcommunity initially began burning the twigs with radio frequencyablation therapies, using the tip of a needle to electrocute the twig.However, radio frequency ablation therapies do not give the surgeon avery good view of the twig and, as such, the pain returned in asignificant percentage of patients as twigs often grew back due toincomplete ablation.

The limited success of radio frequency ablation gave rise to thedevelopment of endoscopic attempts to more completely sever the twig,using an endoscope to bring a small camera and a light source to givethe surgeon a better view of the twig during surgery. This allows thesurgeon to physically cut the twig, rather than burn it throughablation, to ensure that the twig is completely severed and reduce thelikelihood that the pain will subsequently return.

Presently known endoscopic techniques involve inserting a dilator intothe patient, where the dilator has a radiolucent strip to allow thesurgeon to locate the tip of the dilator proximate the twig under X-ray.A sheath is inserted over the dilator, and the dilator is withdrawn fromthe patient. An endoscope is then inserted into the sheath. Prior artendoscope cannula assemblies include 3 distinct channels: i) irrigationsupply and return; ii) endoscopic probe having a camera and a slot forreceiving a coagulator; and iii) a light source. Presently knownendoscopic tools used for coagulating twigs at the transverse processwere adapted from analogous tools developed for disc surgery, and arenot well suited for use in the context of the present invention. Forexample, presently know endoscopic sheaths have a larger diameter thannecessary to perform the function of severing the twig, and the distaltip of the sheath—having been developed for disc surgery—is not welladapted for stable placement on the transverse process.

Methods and apparatus are thus needed which overcome these and otherlimitations of the prior art.

Various features and characteristics will also become apparent from thesubsequent detailed description and the appended claims, taken inconjunction with the accompanying drawings and this background section.

BRIEF SUMMARY

Various embodiments of the present invention relate to methods andapparatus for, inter alia: i) providing a sheath with a distal endconfigured to rest on the transverse process proximate the medial nerveroot branch (twig) in a stable manner; ii) providing a resilientlydeformable spring mechanism for moving the endoscope camera back andforth along the sheath axis proximate the twig in a controlled manner;iii) reducing the overall cross sectional area of the endoscope assemblyby employing optimally shaped fluid ingress and egress channels; iv)providing a novel cannula configuration which facilitates fluid ingressand egress without the need for supplemental suction; v) providing asheath aperture which is substantially parallel to the plane of thecamera (substantially orthogonal to the camera line of sight) to therebyoptimize the endoscopic field of view; and vi) providing a stableplatform for allowing the surgeon to cut through the twig orthogonallyby simply extending and retracting the electrode, either manually orautomatically via a resiliently deformable (e.g., elastomeric) spring.

It should be noted that the various inventions described herein, whileillustrated in the context of a direct visualized rhizotomy (DVR)procedure, are not so limited. Those skilled in the art will appreciatethat the inventions described herein may contemplate any procedure inwhich it is desired to transiently dock or otherwise stabilize anendoscopic device on an anatomical surface.

Various other embodiments, aspects, and features are described ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Exemplary embodiments will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and:

FIG. 1 is a perspective view of a dilator and sheath assembly asintroduced for use in a direct visual rhizotomy (DVR) surgical procedurein accordance with various embodiments;

FIG. 2 is a perspective view of the dilator and sheath assembly asinserted into the patient in a DVR procedure, illustrating the placementof the distal end of the sheath on a transverse process proximate amedial branch of the spinal nerve root in accordance with variousembodiments;

FIG. 3 is a perspective view of a cannula and sheath assembly asintroduced for use in a DVR procedure, illustrating a ribbed cannulaconfiguration in accordance with various embodiments;

FIG. 4 is a perspective view of the cannula and sheath assembly asinserted into the patient in a DVR procedure, illustrating the placementof the distal end of the cannula and sheath assembly on the transverseprocess proximate a medial branch of the spinal nerve root in accordancewith various embodiments;

FIG. 5 is a perspective view of the cannula and sheath assembly of FIG.4, with a bipolar probe inserted through the cannula, in accordance withvarious embodiments;

FIG. 6 is a perspective view of the cannula and sheath assembly of FIG.5, illustrating the manual and/or automatic axial extension of the probeto cut across and thereby coagulate the medial branch in accordance withvarious embodiments;

FIG. 7 is a schematic top view of a vertebral body illustrating theposition of each medial branch on a corresponding transverse process inaccordance with various embodiments;

FIG. 8 is a schematic cross-section view taken along line VIII of FIG.7, illustrating the placement of the sheath on the surface of thetransverse process in accordance with various embodiments;

FIG. 9 is a perspective view of an exemplary DVR endoscopic assemblyincluding a sheath, cannula, endoscope, electrode, and fluid ingress andegress channels in accordance with various embodiments;

FIG. 10 is an exploded perspective view of the assembly of FIG. 9,illustrating the upward looking angle of the camera line of sightrelative to the sheath axis in accordance with various embodiments;

FIG. 11 is a close up view of an exemplary DVR endoscopic assembly,depicting a resiliently deformable spring mechanism for facilitating acontrolled transition between axially extended and retracted camera(and/or electrode) positions in accordance with various embodiments;

FIG. 12 is a perspective view of the DVR endoscopic assembly of FIGS. 9and 11 with the endoscope and electrode removed to highlight variousdetails of the cannula, sheath distal end, and the elastomeric componentin accordance with various embodiments;

FIG. 13 is a schematic view of a sheath having an aperture orthogonal tothe sheath axis in accordance with various embodiments;

FIG. 14 is a schematic view of the sheath of FIG. 13 having an apertureconfigured to remove that portion of the sheath tip which wouldotherwise interfere with the field of view of the camera configured at a“looking up” angle with respect to the sheath axis, such that theaperture defines a plane substantially orthogonal to the camera line ofsight in accordance with various embodiments;

FIG. 15 is a schematic view of a sheath having a distal tip configuredwith a primary cut-away to facilitate a substantially unobstructed viewof the fluid pressure bubble surrounding the surgical site in accordancewith various embodiments;

FIG. 16 is a schematic view of the sheath of FIG. 15, further includinga secondary cut-away to facilitate stable transient placement(“docking”) of the sheath on an anatomical surface in accordance withvarious embodiments;

FIG. 17 is a schematic view of the sheath of FIG. 15 in the dockedposition on a transverse process proximate a cross section view of amedial branch in accordance with various embodiments;

FIG. 18 is a side view of an alternate exemplary sheath illustratingrespective first and second cut-away regions in accordance with variousembodiments;

FIG. 19 is a perspective view of a ribbed cannula structure defining anendoscope channel, an electrode channel, a fluid ingress channel, and afluid egress channel, one or more of which may be configured to bebounded by the inner perimeter of the sheath (not shown in FIGS. 18 and19) in accordance with various embodiments;

FIG. 20 is a partial section view of the cannula of FIG. 19, with aportion of the cannula structure removed to reveal details associatedwith the electrode receiving mechanism in accordance with variousembodiments;

FIG. 21 is a partial section view of the ribbed cannula structure ofFIG. 20 illustrating the fluid ingress channel bounded by a portion ofthe sheath in accordance with various embodiments;

FIG. 22 is schematic cross-section view of a DVR assembly including acannula configuration defining respective endoscope, electrode, fluidingress, and fluid egress wholly contained within the cannula structurein accordance with various embodiments;

FIG. 23 is schematic cross-section view generally to FIG. 22, in whichthe endoscope and electrode channels partially intersect, and furtherwherein the fluid ingress and egress channels are noncircular yet whollycontained within the cannula structure in accordance with variousembodiments;

FIG. 24 is schematic cross-section view of a DVR assembly generallyanalogous to FIGS. 22 and 23, in which the endoscope and electrodechannels partially intersect, and further wherein the fluid ingress andegress channels are partially bounded by the inner wall of the sheath inaccordance with various embodiments;

FIG. 25 is schematic cross-section view of a DVR assembly generallyanalogous to FIGS. 22-24, in which the endoscope and electrode areguided by minimal cannula structure extending radially inwardly from theinner wall of the sheath, and further wherein the fluid ingress andegress channels have an inside boundary defined by one or both of theelectrode and endoscope, and an outside boundary defined by the sheathwall in accordance with various embodiments;

FIG. 26 is a perspective view of a DVR device showing external fluidingress and egress connections for use both with and withoutsupplemental suction in accordance with various embodiments;

FIG. 27 is perspective view of a dilator, a dilator in the sheath, and acannula including an endoscope and electrode in the sheath in accordancewith various embodiments;

FIG. 28 is a perspective exploded view of the components shown in FIG.27 in accordance with various embodiments;

FIG. 29 is a schematic view of an endoscope in the sheath depicting thecamera in a retracted position in accordance with various embodiments;

FIG. 30 is a schematic view of the endoscope in the sheath shown in FIG.29, depicting the camera in an extended position as a result ofcompressing the elastomeric spring in accordance with variousembodiments;

FIG. 31 is a schematic view illustrating the retracted and extendedpositions of the camera shown in FIGS. 29 and 30 in accordance withvarious embodiments;

FIG. 32 is a perspective view of a dilator having a chisel configured toscrape the transverse process or other anatomical surface to provide asecure footing in accordance with various embodiments;

FIG. 33 is a top view of the dilator shown in FIG. 32 in accordance withvarious embodiments; and

FIG. 34 is a side view of the dilator shown in FIG. 32 in accordancewith various embodiments.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit the invention or the applicationand uses of the invention. Furthermore, there is no intention to bebound by any theory presented in the preceding background or thefollowing detailed description.

Various embodiments of the present invention relate devices andassociated methods for performing endoscopic procedure, such as directvisualized rhizotomy in which a small, hair-like nerve branch iscoagulated or otherwise severed to prevent it from transmitting painsignals from a facet joint.

By way of brief introduction, each vertebral body (e.g., lumbarvertebrates L4, L5) in the human spine has an upper extending processand a lower extending process; adjacent upper and lower extendingprocesses together form a facet joint. Every facet joint is innervatedby two hair-like medial nerve branches (referred to herein as twigs),and every medial branch innervates two joints. In addition, eachvertebral body further includes respective left and right transverseprocesses, across which the twig extends. Although the surface of thetransverse process is modeled as a substantially flat, horizontalsurface to facilitate this discussion, those skilled in the art willappreciate that an actual transverse surface is irregular, and generallyconvex.

When the facet joint becomes inflamed, the twig transmits pain signalsto the brain. Rather than attempt to address the source of inflammation,it is sometimes easier to simply sever the twig. Indeed, for somepatients this is the only therapeutic intervention that can providerelief from what is often debilitating, chronic pain.

In an embodiment, a dilator tool is inserted into a sheath, and thedilator/sheath assembly is used to cut thru the patient's skin andunderlying tissue until the terminal end of the assembly is positionedproximate the transverse process. The surgeon then removes the dilator,leaving the sheath in place. Inserting a cannula (including anendoscope) into the sheath provides the surgeon with a live visual ofthe medial branch and surrounding tissue displayed on a screen ormonitor. The endoscope uses a pressurized saline solution (water) todilate the surrounding tissue and create a “bubble” which functions asworking space at the twig site.

With the sheath resting on the transverse process proximate the twig, acoagulating electrode may be inserted through the cannula and extendedto the twig location, whereupon the electrode is actuated to cut acrossthe twig, using the electrode as a dissector. In various embodiments,the sheath and cannula of the present invention may be configured toaccommodate any number of the various industry standard and widelyavailable endoscopes, such as those available from Stryker™ ofKalamazoo, Mich., Medtronic™ of Minneapolis, Minn., and Karl Storz ofGermany.

The boney transverse process (TP) can be seen on the screen using X-rayillumination. To assist the surgeon in placing the distal end of thedevice on the surface of the transverse process, the dilator and/orsheath may include one or more radiolucent markings. In this way, thesurgeon can reliably locate the sheath tip at the twig, knowing that thetwig is located on the transverse process. Once the distal end of thedilator/sheath assembly is maneuvered into position on the transverseprocess, the dilator is removed from the sheath and replaced with thecannulated endoscope, which may be secured in the sheath using a colletlock or any other desired mechanism. The endoscope may then be used todefinitively orient the cauterizer (electrode) at the twig, allowing thesurgeon to affirmatively confirm that the cauterizer cuts through thetwig while watching the nearby screen in real time.

In an embodiment, the cauterizer or coagulator comprises bipolar activeelectrode probe available from Ellman™ International of Hicksville, N.Y.In practice, the surgeon pre-sets the voltage (e.g., 40 millivolts), anduses a pedal, switch, verbal command, or other technique to activate theelectrode once it is in the proper position proximate the twig. Byensuring that no partial contiguity remains after coagulation,cauterization, or otherwise completely cutting through the twig, thepatient can be assured that the nerve cannot recover (grow back). Thatis, although the proximal and distal ends of the medial branch remainconnected to their respective roots, there can be electricaltransmission across the twig after it is cut.

Presently known endoscopic tools do not permit transitioning the camerabetween an retracted position which provides a far field view of thebubble site, and an extended position providing a close up view of thetwig, in part because knee and disc surgical procedures focus on objectssignificantly larger than a twig; hence, there is no need to extend andretract the camera. In accordance with one aspect of the presentinvention, a neoprene spring allows the surgeon to manually orautomatically extend and retract the camera along the cannula axis tocontrollably transition between a far field and near field view of thesit under inspection. This movement allows the surgeon to obtain an upclose view of the region to be cut, then retract the camera to obtain abroader perspective during the actual cutting; alternatively, thesurgeon may view the surrounding tissue at a distance, then bring thecamera in close to the twig during actual cutting.

In an embodiment, the endoscope assembly may include opposing surfaces,handles, loops, or the like for the thumb and a finger (e.g.,forefinger) to squeeze a trigger formed by the opposing surfaces tothereby move the camera from the retracted position to the extendedposition; when thumb/finger pressure is gradually released, theresilient spring returns the camera to the retracted position. Thespring mechanism may be configured to avoid jerky visual artifacts.

In another embodiment, an analogous trigger mechanism may be employed tocontrollably move the electrode tip through the twig during cutting.

In accordance with a further aspect of the invention, the distal end ofthe sheath may be configured to provide an aperture having a size,shape, orientation, and configuration optimized for cutting a twig onthe surface of the transverse process. For example, if the aperture istoo large or at too step an angle relative to the sheath axis, adjacentsoft tissue may obscure the field of view. In an embodiment, a flat orconcave cut-away is made in the distal end of the sheath to create anaperture which looks upwardly, for example in the range of 30° from thesheath axis. Those skilled in the art will appreciate that this allowsthe aperture to remain generally parallel to the plane of the endoscopecamera, which typically tilts upward at a 30° angle from the sheathaxis.

In a preferred embodiment, a secondary cut-away is then formed in thebottom of the sheath, creating a flat or concave surface to rest on theconvex surface of the transverse process during cutting of the twig(whereas a rounded tip tends to roll on the TP surface). Placing acut-out (or “flat”) on the distal end of the angled sheath tip allowsthe sheath to firmly rest on the transverse process. The secondarycut-out can be flat, concave, or any desired geometry to facilitatetransient docking of the device on the TP.

The present inventor has further determined that presently known cannuladesigns do not adequately balance the need for a minimally invasivedevice profile (cross section) with the need to irrigate the surgicalsite to create the working pressure bubble. In particular, usingcircular channels for fluid ingress and fluid egress along the cannularesults in unnecessary cannula structure, which takes up space withinthe sheath which could otherwise be used for irrigation. Accordingly, inan embodiment, non-circular fluid ingress and/or egress channels areemployed to reduce the overall cross sectional profile of the device,while still allowing sufficient fluid flow.

More particularly, the cross-sectional shape of one or both of the fluidingress and egress channels may include two components: i) an arcsegment of outer diameter of one or both of the coagulator and endoscopechannels if these channels are circular in cross-section; otherwise thisfirst component may comprise a segment of the outer perimeter of one orboth of the coagulator and endoscope channels; and ii) an arc segment ofthe sheath inner diameter if the sheath has a circular cross-section;otherwise this second component may comprise a segment of the innerperimeter of the sheath.

By configuring the cross-sectional shape of the ingress and egresschannels to utilize “what's left” after subtracting the (typically)circular cross sectional areas for the coagulator and endoscopechannels, endoscope assembly may occupy a smaller total cross sectionalarea as compared with ingress and egress channels having circular crosssections.

Referring now to FIGS. 1-8, various aspects of the present inventionwill now be described in conjunction with an exemplary direct visualrhizotomy (DVR) surgical procedure.

More particularly, FIG. 1 is a perspective view of a dilator and sheathassembly 100 as these components may introduced for use in a DVRprocedure on a vertebral body no of a human or animal spine 112.Specifically, the dilator/sheath assembly 100 includes a dilator toolhaving a distal tip 102 and a handle 104 slidably disposed within asheath 106. The sheath 106 may include grips 108 to facilitate theinsertion, removal, and manipulation of the dilator, cannula, andendoscope, and electrode, as described in greater detail below.

FIG. 2 includes a first view 201 and a second view 203. The first view201 shows a dilator sheath assembly 200 inserted into the patient suchthat the tip of the dilator/sheath assembly is adjacent a transverseprocess 203. As briefly discussed above, once the tip is in placeproximate the transverse process, the surgeon removes the dilator toallow the cannula to be inserted into the sheath. The second view 203shows the sheath 206 with the dilator removed and before the cannula isinserted into the sheath. As shown in view 203, the vertebral body 210includes a left transverse process 212 having a twig 214 extendingthereacross, and a right transverse process 216 having a twig 218extending thereacross. Note that the tip 202 of the sheath suitablyrests on the transverse process 216 proximate the twig 218. As describedin greater detail below, the tip 202 of the sheath incorporates a first(upper) cut-away configured to provide an optimum field of view for theendoscope camera, and a second (lower) cut-away configured to allow thesheath to rest on the transverse process in a stable manner during thecutting portion of the DVR procedure.

FIG. 3 shows a first view 301 of a cannula having a ribbed shaft 304with an attached endoscope 302 being inserted into a sheath 306previously positioned on the transverse process as described above. FIG.3 also includes a second view 303 showing a close up of an endoscopecamera 310 at the distal end of an endoscope channel, described ingreater detail below.

FIG. 4 includes a first view 401 showing an endoscope 402 receivedwithin an endoscope channel in the cannula shaft (not shown in FIG. 4),with the endoscope and cannula inserted into a sheath 406 such that thedistal tip 420 of the cannula assembly rests on the transverse process.A second view 403 depicts a second cut-away 412 in the sheath tipconfigured to rest on a transverse process surface 408 proximate amedial branch (twig) 410. In an embodiment, the shape (e.g., radius) ofthe concavity of cut-away 412 suitably generally corresponds to theconvexity of the transverse process surface.

Once the surgeon confirms that the tip of the sheath is proximate thetwig, for example by viewing a live feed video monitor displaying theoutput signal from the endoscope camera, a bi-polar probe or other toolfor cutting, coagulating, cauterizing, burning, slicing, cutting, orotherwise severing the twig may be inserted through the cannula to thetwig site. More particularly, FIG. 5 depicts an electrode 530 beinginserted into a cannula assembly 501. FIG. 6 depicts movement 532(either manual or automatic) of a proximal end 535 of the electrode 530along the axis of the endoscope. This movement along arrow 535 resultsin corresponding movement of a distal end 542 of the electrode 530 alongarrows 544 to thereby cut through the twig 546 and complete the DVRprocedure.

FIG. 7 is a schematic top view of a vertebral body 702 having respectiveupper and lower adjacent discs 704 and respective transverse processes706, each having a medial nerve branch (twig) 708 extending thereacross.The above described DVR procedure culminates in cutting the twig alongcut lines 710.

In accordance with various embodiments, the distal end of the sheathincludes two cut-aways: i) a first cut-away configured to position theendoscope camera with an optimal field of view of the twig site; and ii)a second cut-away configured to allow the sheath to rest upon thesurface of the transverse process immediately proximate the twig.

More particularly and referring now to FIG. 8, a schematic cross-sectionview taken along line VIII of FIG. 7 shows the placement of the sheathon the surface of the transverse process in accordance with variousembodiments. In the illustrated embodiment, a sheath 810 comprises afirst cut-away 812 configured to afford the endoscope camera (not shownin FIG. 8) an unobstructed line of sight to the twig 808, and a secondcut-away 814 configured to rest on the surface 806 of the transverseprocess.

FIG. 9 is a perspective view of an exemplary DVR endoscopic assembly 900including an endoscope 902 and an electrode 904 secured within a cannula(not shown inside a sheath 906 having a barbed 908 shaft. The distal endof the sheath (lower left in FIG. 9) includes a first cut-away 912, asecond cut-away 914 comprising two prongs configured to allow the sheathto dock on the surface of a transverse process, an endoscope camera 918,a fluid ingress channel 920 and a fluid egress channel 922.

FIG. 10 is an exploded perspective view 1000 of the assembly of FIG. 9,including an endoscope 1002 having a shaft 1022 defining a longitudinalaxis 1026, and a camera 1024 having a line of sight along a sight axis1028 inclined upwardly from the axis 1026 at an angle 1030. In anembodiment, the angle 1030 is in the range of 5 to 75 degrees, andpreferably in the range of 20 to 60 degrees, and most preferably about30 or 45 degrees.

With continued reference to FIG. 10, view 1000 further includes a ribbedcannula configured to receive endoscope 1002 and an electrode 1004 forreceipt within a sheath 1006 having a longitudinal axis 1036, and aresiliently deformable spring 1020 configured to facilitate controlledmovement of the camera (and the electrode, if desired) along the sheathaxis 1036, as described in greater detail below. The distal end of thesheath 1006 includes a first cut-away 1042 defining an aperture orientedsubstantially orthogonal to a line of sight 1038. In a preferredembodiment, an angle 1040 defined between the axis 1036 and the line ofsight 1038 corresponds to the angle 1030, so that the camera faceremains substantially parallel to the plane defined by the firstcut-away 1042.

FIG. 11 is a close up view of an exemplary DVR endoscopic assembly 1100,including a resiliently deformable spring mechanism 1111 forfacilitating a controlled transition between axially extended andretracted camera (and/or electrode) positions in accordance with variousembodiments. In the illustrated embodiment, an electrode 1104 can beconveniently inserted into and removed from an electrode inlet 1106 toguide the electrode into an electrode channel (not shown in FIG. 11)formed in the cannula, as described in greater detail below.

FIG. 12 is a perspective view of an exemplary DVR endoscopic with theendoscope and electrode removed to highlight various details of thecannula 1202 disposed inside the sheath 1206. An exemplary spring 1212is also shown.

FIG. 13 is a schematic view of a sheath having an aperture orthogonal tothe sheath axis in accordance with various embodiments. Moreparticularly, a sheath 1302 defines a longitudinal axis 1304. Anendoscopic camera 1306 mounted within the sheath is configured to have aline of sight along an axis 1308, defining an angle 1310 with respect tothe axis 1304. The value of the angle 1310 is generally analogous to theangle 1030 discussed above in conjunction with FIG. 10, namely about30°.

FIG. 14 is a schematic view of the sheath of FIG. 13 having an apertureformed by a first cut-away disposed at an angle 1410 (parallel to aplane 1408) with respect to a vertical plane 1404. The value of theangle 1408 is generally analogous to the angle 1310, such that a camera1406 provides an unobstructed view out the aperture. In this way, thefirst cut-away is configured to remove that portion of the sheath tipwhich would otherwise interfere with the field of view of the camera.

FIG. 15 is a schematic view of a sheath having a distal tip configuredwith a primary cut-away to facilitate a substantially unobstructed viewof the fluid pressure bubble surrounding the surgical site in accordancewith various embodiments. In particular, a sheath 1502 includes aprimary (or first) cut-away 1504 disposed along a line 1508 inclined anangle 1512 with respect to a vertical plane 1510. Alternatively, theprimary cut-away may comprise a concave surface 1506. The value of theangle 1512 generally corresponds to the angles 1310 and 1498, describedabove.

FIG. 16 is a schematic view of the sheath of FIG. 15, further includinga secondary cut-away to facilitate stable transient placement(“docking”) of the sheath on an anatomical surface (e.g., a transverseprocess) in accordance with various embodiments. In particular, a sheath1602 includes a primary cut-away 1604 and a secondary cut-away 1620disposed along a line 1622 inclined at an angle 1626 with respect to ahorizontal line 1624 parallel to the longitudinal axis of the sheath.The angle 1626 generally corresponds to the angle at which the DVRassembly is inserted into the patient, typically in the range of 45 to75 degrees relative to a horizontal plane, and preferable about 60degrees from a horizontal plane (about 30 degrees from a verticalplane).

FIG. 17 is a schematic view of the sheath of FIG. 16 in the dockedposition on a transverse process 1704 proximate a cross section view ofa medial branch 1706 in accordance with various embodiments. Inparticular, a sheath 1702 has a longitudinal axis 1708, a first cut-away1705, and a second cut-away 1707 generally corresponding to the firstand second (primary and secondary) cut-aways, respectively, describedabove in conjunction with FIG. 16.

Also shown in FIG. 17 is an endoscope camera 1710, having a line ofsight 1712 suitably inclined at an angle 1730 (e.g., 30 degrees)relative to the axis 1708. As such, the camera remains generallyparallel to the aperture defined by the primary cut-away 1705, andmaintains an appropriate angle (e.g., 30 degrees) relative to the sheathaxis. Consequently, when the surgeon inserts the endoscope assemble intothe patient at 60 degrees from a horizontal plane (30 degrees from avertical planeo, as is typical, the surface 1707 of the sheath may beconveniently stabilized on the (substantially horizontal) surface 1704of the transverse process.

FIG. 18 is a side view of an alternate exemplary sheath 1800illustrating a first cut-away region 1802 and a second cut-away region1804 in accordance with an alternate embodiment.

FIG. 19 is a perspective view of a ribbed cannula structure 1900defining an endoscope channel 1902, an electrode channel 1904, a fluidingress channel 1906, and a fluid egress channel 1908, one or more ofwhich may be configured to be bounded by the inner perimeter of thesheath (not shown in FIG. 19) in accordance with various embodiments. Byusing the inner wall of the sheath as a partial boundary of the fluidingress and egress channels, the total cross sectional area of thesheath may be reduced while still providing adequate cross sectionalarea for irrigation.

FIG. 20 is a partial section view of the cannula of FIG. 19, with aportion of the cannula structure removed to reveal details associatedwith the electrode receiving mechanism in accordance with variousembodiments. More particularly, a cannula structure 2000 includes anendoscope channel 2002 (partially removed), a fluid ingress channel2006, an electrode channel 2004 (partially removed, and an electrodeintake chute 2012 configured to allow the surgeon to manually insert theelectrode into the electrode channel 2004. In the illustratedembodiment, the cannula structure 200 includes respective lobes 2008,2010 having convex radii configured to mate with the inner perimeter ofthe sheath wall to form a fluid seal bounding the fluid ingress channel2006.

FIG. 21 is a partial section view of the ribbed cannula structure 2100,illustrating the fluid ingress channel bounded by an arc segment 2104 ofsheath 2102.

Various configurations for arranging the aforementioned channels withinthe sheath will now be described in conjunction with FIGS. 22-25.Although the illustrated embodiments depict a sheath having a circularcross section (for example, taken along line IX-IX of FIG. 9), it willbe appreciated that the present invention contemplates a sheath havingany cross-sectional shape including circular, elliptical, tear drop, andthe like. Moreover, while the endoscope and electrode channels areillustrated as having a circular cross section, it will be understoodthat the invention contemplates endoscopes, electrodes, and/or theirassociated channels of any suitable cross-sectional shape, size, andconfiguration.

FIG. 22 is schematic cross-section view of a DVR assembly 2220 includinga cannula 2200 coaxially disposed within a sheath 2202, the sheathhaving an inner perimeter 2203 and an outer perimeter 2205. The cannula2200 comprises discrete channels, each completely bounded by the cannulastructure and defining: i) an electrode channel 2204 having an electrode2206 received therein; ii) an endoscope channel 2212 having an endoscope2214 received therein; iii) a fluid ingress channel 2208; and iv) afluid egress channel 2210. In the illustrated embodiment, the electrodehas an outer diameter (OD) in the range of 2.5 millimeters (mm), and theendoscope has an OD in the range of 4 mm.

The present inventor has determined that using wholly contained circularchannels for the irrigation channels unnecessarily increases the overallcross-sectional area of the DVR assembly, and therefore proposes variousalternate embodiments comprising non-circular irrigation channels toreduce the overall cross-sectional area of the device, while maintainingadequate fluid flow. Indeed, the present inventor has further determinedthat by providing a fluid egress channel with sufficient cross-sectionalarea, supplemental suction may be eliminated entirely; that is, thepressure of the fluid ingress channel is sufficient to urge the fluidback through the device and out of the system.

Referring now to FIG. 23, a DVR assembly 2320 includes a sheath 2302surrounding a cannula 2304, the cannula defining an electrode channelpartially intersecting an endoscope channel 2308, both of which arestructurally (and, hence, hydraulically) isolated from respective fluidingress and egress channels 2310 and 2312. Note that the non-circularfluid ingress and egress channels are configured to efficiently utilizethe cross sectional within the inner perimeter of the sheath which isnot occupied by the electrode and endoscope channels.

FIG. 24 depicts a DVR assembly 2420 including a sheath 2402 surroundinga cannula, the cannula comprising a first partition 2406 defining afluid ingress channel 2422, and a second partition 2408 defining a fluidegress channel 2420. In the illustrated embodiment, the fluid channel ispartially bounded by a cannula partition, and partially bounded by asegment of the inner sheath wall, for example an arc segment 2414extending between lines 2410 and 2412. To provide hydraulic isolation,each cannula partition may include one or more extensions which contactthe sheath, such as regions 2416 and 2418 which substantially seal thefluid channel.

FIG. 25 is schematic cross-section view of a DVR assembly 2520 includinga sheath 2502 surrounding a cannula which includes an electrode guide2508, an endoscope guide 2510, and a common guide 2512. Together, thethree guides, the endoscope, the electrode, and the inner sheath walldefine a fluid ingress channel 2504 and a fluid egress channel 2506.

FIG. 26 is a perspective view of a DVR device including external fluidingress and egress connections 2602, 2604 to the aforementionedirrigation channels. Note that the fluid connections and the irrigationchannels may be configured for use either with or without supplementalsuction.

FIG. 27 is perspective view of a dilator 2702 standing alone, and thedilator 2702 inserted into a sheath 2704. FIG. 27 further depicts thesheath 2704 with the dilator removed, and replaced by a cannula 2708having an endoscope 2706 and an electrode 2710 inserted therein.

FIG. 28 is a perspective exploded view of a DVR assembly 2800 inaccordance with various embodiments. In particular, the DVR 2800comprises an endoscope including an endoscope handle 2818, an endoscopeshaft 2810, and an endoscope camera 2822 mounted to the distal end ofthe shaft. DVR 2800 further includes a cannula assembly including acannula top cap 2802, a septum seal 2804, and a ribbed cannula shaft2806 defining channels for the endoscope, electrode, and irrigation. Asdescribed above, once the dilator 2808 us used to guide the sheath intoplace proximate the transverse process, the dilator is removed and thecannula in inserted into the sheath. In the illustrated embodiment, thecannula assembly may be secured within the sheath 2816 using an outercover 2810, a wiper seal 2812, and an elastomer spring 2814. The mannerin which the spring functions to controllably extend and retract thecamera is described in greater detail below in conjunction with FIGS.29-31.

FIG. 29 is a schematic view of a spring actuated camera assembly 2900comprising a sheath 2912 having a primary cut-away 2918 and a secondarycut-away 2920 disposed proximate a twig 2916 on the surface of atransverse process 2914. A thumb mount 2902 is connected to an endoscope2908, and an opposing forefinger mount 2904 is connected to the sheath.A spring 2906 is disposed between the thumb and forefinger mounts, suchthat urging them toward one another extends the camera 2910 downwardlyalong the sheath to obtain a close-up view of the twig.

FIG. 30 is a schematic view of the spring actuated camera assembly ofFIG. 29, showing the camera 3010 in an extended position closer to thetwig 3016 as a result of squeezing the trigger 3002 and therebycompressing the spring. Releasing the trigger 3002 returns the camera tothe retracted position shown in FIG. 29, due to the resilientlydeformable character of the spring.

FIG. 31 is a schematic view showing both the retracted 3102 and extended3104 camera positions within the sheath 3112, with the two positionsseparated by a distance 3106 in the range of 0.1 to 100 mm, andpreferably between 0.5 and 10 mm, and most preferably about 2 to 3 mm.

FIG. 32 is a perspective view of an alternative embodiment of a dilator3200 having a chisel configured 3202 to scrape the transverse process orother anatomical surface to provide a secure footing during a DVR orother procedure. More particularly, as shown in FIGS. 33 and 34, thechisel 3202 comprises a concave scraping blade 3404 extending betweenrespective pointed prongs 3303, 3305. During a DVR procedure, the chiselend 3202 may be used to facilitate insertion of the dilator through thepatient's skin. Once the dilator is guided into a position proximate thetransverse process, the chisel may used to scrape a small region on thetransverse process to thereby provide a secure footing for the sheath torest upon after the dilator is removed from the sheath and replace bythe cannula, as described above.

While the present invention has been described in the context of a DVRprocedure in which the device is place proximate the transverse processto facilitate cutting the twig, it will be appreciated that theinvention is not so limited. For example, the size, shape,configuration, and relative positions of the sheath, cannula,resiliently deformable spring material and other components may bevaried to accommodate virtually any procedure in which it is desirableto place the distal end of the sheath on any anatomical surface tostabilize the device during an endoscopic procedure. Moreover, althougha coagulating electrode has been described, it will be understood thatany mechanism including mechanical (scissors, knife), thermal (resistiveheating element), or optical (e.g., a laser) components may be employedwithin the scope of the present invention.

An elongated tubular sheath is thus provided for use in endoscopicsurgery. The sheath includes: a proximal end configured to removablyreceive a cannula; a distal end; a horizontal shaft having alongitudinal axis extending between the proximal end and the distal end;a first cut-away generally defining a first plane at the distal end, thefirst cut-away characterized by a first angle relative to a verticalplane; and a second cut-away generally defining a second plane at thedistal end, the second cut-away characterized by a second angle relativeto a horizontal plane; wherein the first cut-away has a substantiallygreater surface area than the second cut-away.

In an embodiment, the first cut-away comprises an aperture for anendoscope camera, and the second cut-away comprises a seat for restingthe sheath on an anatomical structure.

In an embodiment, the first angle has a value in the range of 15 to 45degrees, and preferably approximately 30 degrees.

In an embodiment, the second angle has a value in the range of 15 to 45degrees, and preferably approximately 30 degrees.

In an embodiment, one or both of the first and second cut-aways form aconcavity when viewed from outside the sheath.

In an embodiment, the first cut-away intersects the second cut-away at athird angle in the range of 90 to 150 degrees, and preferably about 90degrees.

In an embodiment, the sheath further includes an endoscope cameradisposed at the distal end, the camera having a line of sightsubstantially orthogonal to the first plane.

In an embodiment, the sheath further includes a radiolucent markingproximate the distal end.

In an embodiment, the sheath further includes two prongs disposed at anintersection between the first and second planes.

A method of manufacturing a sheath for use in endoscopic surgery is alsoprovided. The method includes: providing a horizontal shaft having alongitudinal axis extending between a proximal end and a distal end;forming a first surface at the distal end, the first surfacecharacterized by a first angle relative to a vertical plane; and forminga second surface at the distal end, the second surface characterized bya second angle relative to a horizontal plane; wherein the first andsecond angles are in the range of about 30 degrees, and the firstsurface has a substantially greater surface area than the secondsurface.

A method is also provided for stabilizing an endoscopic assembly on aninternal anatomical surface during surgery. The method includes:providing a tubular sheath having an axis and a distal end, the distalend including a first surface defining an aperture and a second surfacedefining a docking land, the first and second surfaces each inclinedrelative to the axis at respective angles in the range of about 45 to 75degrees; inserting the distal end of the sheath into a patient;inserting an endoscope into the sheath and disposing an endoscope cameraproximate the aperture; displaying a signal received from the camera ona screen; and using the displayed signal to maneuver the docking landonto the anatomical surface.

In an embodiment, the method further includes: equipping the endoscopicassembly with an actuator; and manipulating the actuator to move thecamera a predetermined distance from a retracted position to an extendedposition while the docking land is disposed on the anatomical surface.

In an embodiment, the actuator comprises a spring, wherein manipulatingthe actuator comprises squeezing the trigger to compress the spring.

In an embodiment, moving the camera to the extended position causes thedisplayed signal to provide a close-up view of the anatomical surface.

In an embodiment, the method further includes: inserting a cutter intothe endoscopic assembly; and using the cutter to sever tissue on theanatomical surface while the docking land rests on the anatomicalsurface.

In an embodiment, the cutter comprises an electrode, the anatomicalsurface comprises a transverse process of a vertebral body, and thetissue comprises a medial branch of a spinal nerve root, and furtherwherein severing the tissue comprises extending the electrode beyond thedistal end of the sheath to thereby cauterize the medial branch.

In an embodiment, the predetermined distance is in the range of 0.5 to10 millimeters, and preferably about 2 to 3 millimeters.

An apparatus is also provided for performing endoscopic surgery. Theapparatus include: an endoscope of the type including a camera disposedat a distal end of an endoscope shaft; a tubular sheath having alongitudinal axis and configured to slidably receive the endoscopetherein such that the camera is disposed proximate a distal end of thesheath; and an actuator configured to toggle the camera between apredetermined retracted position and a predetermined extended positionalong the sheath axis.

In an embodiment, the actuator includes a trigger configured to besqueezed between a user's thumb and forefinger.

In an embodiment, the trigger includes a first surface connected to theendoscope and a second surface connected to the sheath, such that urgingthe first surface relative to the second surface causes the camera tomove relative to the sheath.

In an embodiment, the distance between the predetermined retractedposition and the predetermined extended position is in the range ofabout 0.5 to 10 millimeters, and preferably about 2 to 3 millimeters.

In an embodiment, the distal end of the sheath includes an aperturesubstantially parallel to the camera line of sight and a surfaceconfigured to facilitate docking the sheath on an anatomical surface.

In an embodiment, the apparatus further includes a spring configured toresiliently deform in response to actuation of the actuator.

In an embodiment, the spring comprises an elastomeric annulus.

In an embodiment, the spring is disposed between the sheath and a handleportion of the endoscope.

A cannula is also provided for use in an endoscopic surgical apparatusof the type including a tubular sheath having an inner wall. The cannulaincludes: a first channel configured to receive an endoscope shaft; afluid ingress channel; and a fluid egress channel; wherein at least oneof the fluid ingress and fluid egress channels comprise a non-circularcross section.

In an embodiment, the cannula is configured such that, when the cannulais received within the sheath, a portion of one of the fluid ingress andfluid egress channels is bounded by the inner wall.

In an embodiment, the cannula is configured such that, when the cannulais received within the sheath, a portion of the fluid ingress channeland a portion of the fluid egress channel is bounded by the inner wall.

In an embodiment, both the fluid ingress and fluid egress channelscomprise a non-circular cross section.

In an embodiment, the cannula further includes a second channelconfigured to receive an elongated cutter.

In an embodiment, the first and second channels partially intersect.

In an embodiment, a portion of one of first and second channels isbounded by the inner wall.

A cannula is also provided for use in an endoscopic surgical apparatusof the type including a tubular sheath having an inner wall. The cannulaincludes: a first channel configured to receive an endoscope shaft; asecond channel configured to receive an elongated cutter; a thirdchannel configured for fluid ingress; and a fourth channel configuredfor fluid egress; wherein a portion of each of the first, second, third,and fourth channels is bounded by the inner wall.

In an embodiment, at least one of the third and fourth channels comprisea non-circular cross section, and wherein the cross sectional area ofthe fourth channel is greater than the cross sectional area of the thirdchannel.

In an embodiment, the cross sectional area of the fourth channel issufficient to permit fluid egress without supplemental suction.

In a surgical apparatus including a cannula and a surrounding sheath,the sheath having an internal perimeter defining a total cross sectionalarea, and the cannula comprising a first channel having a firstcross-sectional area for receiving an endoscope and a second channelhaving a second cross-sectional area for receiving a cutting element, amethod is provided for configuring a remaining cross sectional area forfluid ingress and fluid egress. The method includes the steps of:determining a value for the remaining cross sectional area bysubtracting the first cross sectional area and the second crosssectional area from the total cross sectional area; and determining,using a computer: i) a fluid ingress cross sectional shape having acorresponding fluid ingress cross sectional area; ii) a fluid egresscross-sectional shape having a corresponding fluid egress crosssectional area; and iii) a cannula cross sectional shape having acorresponding cannula cross sectional area; wherein the remaining crosssectional area equals the sum of the fluid ingress cross sectional area,the fluid egress cross sectional area, and the cannula cross sectionalarea.

In an embodiment, determining the cannula cross-sectional shape, thefluid ingress cross-sectional shape, and the fluid egresscross-sectional shape involves: first determining at least one of thefluid ingress and fluid egress cross-sectional shapes, and thereafterdetermining the cannula cross-sectional shape based on the previouslydetermined at least one of the fluid ingress and fluid egresscross-sectional shapes.

In an embodiment, determining the cannula cross-sectional shape, thefluid ingress cross-sectional shape, and the fluid egresscross-sectional shape involves: first determining the cannulacross-sectional shape, and thereafter determining at least one of thefluid ingress and fluid egress cross-sectional shapes based on thepreviously determined cannula cross-sectional shape.

In an embodiment, at least one of the fluid ingress and fluid egresscross sectional shapes are non-circular.

In an embodiment, at least one of the fluid ingress and fluid egresscross sectional areas are partially bounded by the cannula and partiallybounded by the sheath internal perimeter.

In an embodiment, the fluid egress cross sectional area is greater thanthe fluid ingress cross sectional area.

In an embodiment, the cannula includes: respective first and secondsegments configured for sliding contact with the sheath internalperimeter and defining therebetween a region of the fluid ingress crosssectional area which is bounded by the sheath internal perimeter; andrespective third and fourth segments configured for sliding contact withthe sheath internal perimeter and defining therebetween a region of thefluid egress cross sectional area which is bounded by the sheathinternal perimeter.

In an embodiment, the cannula shape comprises a FIG. 8.

In an embodiment, the sheath internal perimeter comprises a circularcross section.

In an embodiment, the sheath internal perimeter comprises a non-circularcross section.

An endoscopic surgical apparatus includes an endoscope having a cameradisposed at a distal end of an endoscope shaft, the camera characterizedby a line of sight tilted upwardly by a tilt angle relative to theshaft. The apparatus further includes an elongated tubular sheathcomprising: a proximal end configured to removably receive the endoscopeshaft; a distal end; a horizontal tubular sheath shaft portion having alongitudinal axis extending between the proximal end and the distal end;and an aperture substantially orthogonal to the camera line of sight.

As used herein, the word “exemplary” means “serving as an example,instance, or illustration.” Any implementation described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other implementations, nor is it intended to beconstrued as a model that must be literally duplicated.

While the foregoing detailed description will provide those skilled inthe art with a convenient road map for implementing various embodimentsof the invention, it should be appreciated that the particularembodiments described above are only examples, and are not intended tolimit the scope, applicability, or configuration of the invention in anyway. To the contrary, various changes may be made in the function andarrangement of elements described without departing from the scope ofthe invention.

The invention claimed is:
 1. A method of stabilizing an endoscopicassembly on an internal anatomical surface during surgery, comprising:providing a tubular sheath having an axis and a distal end, the distalend including a first surface defining an aperture and a second surfacedefining a docking land, the first and second surfaces each inclinedrelative to the axis at respective angles in the range of about 45 to 75degrees; inserting the distal end of the sheath into a patient;inserting an endoscope into the sheath and disposing an endoscope cameraproximate the aperture; displaying a signal received from the camera ona screen; and using the displayed signal to maneuver the docking landonto the anatomical surface.
 2. The method of claim 1, furthercomprising: equipping the endoscopic assembly with an actuator; andwhile the docking land is disposed on the anatomical surface,manipulating the actuator to move the camera a predetermined distancefrom a retracted position to an extended position.
 3. The method ofclaim 2, wherein the actuator comprises a spring, and further whereinmanipulating the actuator comprises squeezing a trigger to compress thespring.
 4. The method of claim 2, wherein moving the camera to theextended position causes the displayed signal to provide a close-up viewof the anatomical surface.
 5. The method of claim 2, wherein thepredetermined distance is in the range of about 2 to 3 millimeters. 6.The method of claim 2, further comprising: inserting a cutter into theendoscopic assembly; and using the cutter to sever tissue on theanatomical surface while the docking land rests on the anatomicalsurface.
 7. The method of claim 6, wherein the cutter comprises anelectrode, the anatomical surface comprises a transverse process of avertebral body, and the tissue comprises a medial branch of a spinalnerve root.
 8. The method of claim 7, wherein severing the tissuecomprises extending the electrode beyond the distal end of the sheath tothereby cauterize the medial branch.
 9. The method of claim 6, furthercomprising: after severing the tissue, removing the endoscope from thesheath; and after removing the endo scope from the sheath, removing thesheath from the patient.
 10. The method of claim 1, further comprising:inserting a cannula into the sheath while the distal end of the sheathis inside the patient; wherein inserting the endoscope into the sheathcomprises inserting the endoscope into an endoscopic channel of thecannula.
 11. The method of claim 10, wherein the cannula furthercomprises a fluid ingress channel and a fluid egress channel, the methodfurther comprising: pumping fluid into the ingress channel to therebymaintain an expanded fluid bubble in the tissue proximate the camera.12. The method of claim 1, wherein the docking land comprises asubstantially flat surface.
 13. The method of claim 1, wherein at leasta portion of the docking land comprises a substantially concave surface.14. A method of facilitating a direct visualized rhizotomy (DVR)surgical procedure on a human patient, comprising: providing anendoscopic assembly including a sheath, a camera, and a cutter, whereinthe distal end of the sheath comprises: i) a docking land cut at a firstangle with respect to a longitudinal axis of the sheath; and ii) anoppositely disposed aperture cut at a second angle with respect to thelongitudinal axis such that a line of sight associated with the camerais inclined away from the docking land; inserting the distal end of theendoscopic assembly into the patient; displaying a visual feed from thecamera; using the visual feed to stabilize the docking land on atransverse process proximate a twig; and severing the twig using thecutter.
 15. The method of claim 14, wherein the first angle is in therange of 45° to 75°.
 16. The method of claim 14, further comprising:providing the endoscopic assembly with a toggle mechanism; and manuallyactuating the toggle mechanism to move the camera back and forth alongthe longitudinal axis to thereby extend and retract the camera.
 17. Themethod of claim 16, wherein the toggle mechanism comprises a springloaded trigger.
 18. The method of claim 14, further comprising:providing the endoscopic assembly with at least one fluid channel; andpumping fluid through the at least one fluid channel to thereby maintaina fluid bubble in the vicinity of the twig.
 19. The method of claim 14,wherein the sheath comprises an inner wall, and the endoscopic assemblyfurther comprises a cannula having a first lobe and a second lobedefining a fluid channel therebetween and partially bounded by the innerwall.
 20. A method of stabilizing an endoscopic assembly on an internalanatomical surface during surgery, comprising: providing a tubularsheath having a sheath axis and a distal end including a docking landinclined relative to the sheath axis at an angle in the range of about45 to 75 degrees; inserting the distal end of the sheath into a patient;stabilize the docking land on a transverse process proximate a twig;inserting a tool through the sheath; and severing the twig with thetool.